Hello everyone,

While I have built several ARs over the years but I have always bought complete uppers. I am configuring my first SBR. The parts I am using are a Crosshill Technologies XRS2 side charging billet upper and a Spinta Precision 8" 300 BLK barrel. I have read a great degree on the subject of AR head spacing and it seems like the verdict is split. Some say that its not required, that everything should be built to spec and the head spacing is something you can't change or adjust anyway. Many report that they have never experienced head spacing issues on tons of builds even though they check anyway. Some say better safe than sorry. My understanding is the head spacing occurs when the barrel extension and barrel are mated. I contacted the barrel maker and they said they check head spacing on all their rifle barrels before they ship but my bolt carrier and upper came separate from Crosshill, not the barrel maker. Here is where I stand now. I don't plan on building any more 300 BLK rifles after this one so I have ruled out building my own Go / No Go gauges for $60-$70. I found a company that rents them. Including round trip shipping it would cost me $24. Is it worth it to incur that cost and trouble to check it or do you think its a waste of money?

Thanks for your feedback
Jason

You are far more likely to have headspace issues from an out of spec bolt, but there are plenty of folks here that have had barrels from reputable manufacturers with chamber issues as well.

It's $55 for a set of head space gauges. A very small portion of the price of the gun and worth checking.


I built a 308 that wouldn't headspace. The bolt face was out of spec. Damn glad I found that out before I pulled the trigger.


-Stooxie

Where can you get a set of 300 blk gauges for $55?

You can buy the gauges for a total of $58 right now at Brownells.

I just bought a barrel from Ebay a few weeks ago that the bolt wouldn't close on a go-gauge. For the price of the go-gauge, it is well worth your time and effort to headspace every build you do. If you want, just buy a go gauge and check to see if the bolt closes on it. If it does, take some scotch tape and put it on the back of the gauge. One piece will add about .002 and two pieces will obviously add about .004. This will now be your no go gauge. I've done it this way ever since I saw Gordy Gritters video on barrel chambering and headspacing. If you want you can fast forward the video to 1:40 to see exactly what I'm talking about. Good luck with the build and remember, safety first!

https://www.youtube.com/watch?v=KICBv-0U87Y

http://www.mansonreamers.com/

Thanks for the replies all. It looks like Brownells after shipping would cost me $65.95 for the two gauges. I think I may have to go the rental route for $24 but I will do it.

Thanks
Jason

Who rents head space gauges?



 

There are a couple companies I ran across but this one is the cheapest:

www.reamerrentals.com

They charge $7 for the rental of a set of Go / No Go gauges and then its $17 for round trip USPS Priority mail shipping. So you pay $24, they send you gauges, you keep them three days and then send them back with USPS label they include with gauges. Seems pretty painless and since I am not going to build any more 300 BLK it will save me some cash. I could buy gauges for $66 then resell for a small loss and probably save a couple bucks in the end but the rental route may be less hassle.

Brownells has the go gauge for $29.00. If you use the tape on it for the no go gauge, you could sell the gauge when you're done or just throw it on the shelf for about the same price you will pay to rent it. Plus you get to do the headspacing at your leisure. Your choice.

http://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/go-300-blackout-headspace-gauge-sku100011283-27266-112624.aspx

I like the idea of just using a Go gauge for both using the tape method but I just don't know how well it would work with an AR. Afterall, there is no bolt handle to close like on the bolt gun in the photo. Your really just looking to see if the bolt is level with the upper receiver. Not quite as accurate as I would like IMO. But I never tried, so I don't know for sure.

I’m ordering Manson Precision in 5.56/.223 & .308 & then im done with it. Hows does the saying go "Buy once cry once"  LOL

That's what I'm thinking. The sting from the $66 will be forgotten before the package shows and then I will have what I need. Who knows, maybe I'll build another down the road.

Ok so I got the GO and NO GO gauges. Everything went great! Go gauge in the bolt closed the whole way. NO GO gauge in and bolt would not seat. I am confident with the results and ready to go shooting. I have a friend who is also building a 300 blk. I lent him the gauges today and his bolt will not close on either gauge. Not the GO nor the NO GO gauge. I was thinking he had to narrow down which part is out of spec by tearing down another bolt and trying it or bringing his bolt carrier over to my house and trying on my upper. He found a thread here on AR15.com that a couple posters said it was not a big deal if it didn't close on a GO gauge and they just means there are tight tolerances and it would losen up a little in time. Any thoughts here? If this is the case, why did I even buy a GO gauge? Any thoughts or insight would be appreciated.

Thanks

Yeah, people here post all sorts of insanity. There was one dude complaining that his 308 bolt didn't seat properly (or smoothly) and someone said, "No worries, just slam it home 100 times or so and let the teeth grind their way into the barrel extension." You could hear the cringing of 1000 readers.
I don't want to derail this thread by trouble shooting your friend's build (start another thread for that), but the gauges did exactly what they are supposed to do. If it didn't close on the Go gauge then, as you said, figure out why. Starting with a different bolt is the right approach.
ETA: I suppose I should add, before someone else corrects me, that just because it didn't close on the Go gauge the gun is guaranteed to blow sky high when you shoot it. If you have a match chamber with a match BCG, match this, match that, it might all be so dang tight that the bolt won't close on the Go gauge. I've seen that myself, and using a different BCG corrected the issue. That same BCG closed just fine in a non-match barrel. Cartridge cases are brass and they will comply with the steel. That said, you better know what you're doing if you are going for that kind of tightness. Most people are just buying the hype and not realizing that many of these match components are machined differently from mil-spec, which is intended to be more tolerant. People that build lots of guns will tell you that they definitely encounter non-workable parts. Manufacturers replace stuff all the time. (and that's assuming the gun was built correctly to being with.)
-Stooxie
 

Forster says that a GO gauge verifies that a bolt and barrel combination will chamber a cartridge at SAAMI maximum dimensions.  I consider this an "absolute minimum" chamber.  But there is some validity to when folks say "it's OK if the bolt doesn't close on a GO gauge," if they are willing to accept that their new chamber may be really shallow.  But how shallow are you willing to accept?  To me, that's essentially saying "I'm using a gauge, but I'm going to ignore what it means," or even "I don't bother with that gauge because I'd just ignore what it means anyway."

My first 300 Blackout barrel wouldn't let the bolt get all the way into the barrel extension... by a LOT.  That's NOT OK!!!!!.  The vendor took it back and got me a properly chambered barrel very quickly - and returned the whole lot of those barrels he bought to the manufacturer since they were all improperly chambered.  This stuff does happen.

From what my friend said, the GO and NO GO gauge seated about the same distance from closing. He is going to bring is bolt already tore down to my place tomorrow to try in my upper. If it seats then it's likely his barrel. If it doesn't, he will tear down another bolt and try in his upper.

OK, His bolt closed with the GO gauge on my 300 BLK upper so it looks like its his barrel. He is going to go home with a bore brush and try to clean up chamber. If it does not close after that, he will contact barrel maker for a replacement.

Thanks
Jason

Friend called barrel maker and he sent him a return label and is going to send a replacement. So it all looks like its going to work out. He should have replacement barrel by the end of my next.

Did you rent him the gauges since you saved his butt on his barrel?

No, lol, I should have. All this debate on spending $66 or not and it ended up saving his butt free of charge. Oh well, I think I will hold onto them as I am thinking I might need a 16" 300 blk sooner or later too.